1. Field of the Invention
In one aspect this invention relates to semitrailer construction. In yet a further aspect this invention relates to safety guards used to minimize injuries in rear impacts where a smaller vehicle impacts a semitrailer.
2. Prior Art
The rear of semitrailers is located at an elevated level when compared to the front of normal passenger vehicles. While cars are required to have a standard bumper located within set guidelines to minimize the damage caused when cars collide, large trucks do not presently have such a standard. Thus when a car impacts the rear of a semitrailer, the car tends to continue under the trailer frame. Some have called the present structure a moving guillotine because of the tendency of passenger vehicles to go under the trailer frame and injure the vehicle's occupants even at relatively low speeds. Remedial regulation has been proposed.
It would be desirable to have an auxiliary protection device attached to the rear of a semitrailer which would resist the tendency of passenger vehicles to go under a trailer upon impact in order to provide an increased measure of safety. In addition it would be desirable for the device to absorb energy incrementally so as to minimize vehicle damage at low speeds but have sufficient energy absorption to safely prevent incursion at moderate speeds. Certain military type trailers have additional conditions which must be met. Military vehicles are air lifted to positions near their ultimate destination. The loading ramps for military cargo planes are very steep and if a semi-trailer having an auxiliary bumper is backed up the ramp the auxiliary bumper will probably interfere with the ramp causing damage to the bumper and or the loading ramp. Because military deployment is frequently done under severe time constraints, it would be even more desirable to have a safety bumper system which will move to a noninterfering position upon contact with a ramp but remain deployed when contacted with the shock force of a rear end collision.